Re: mmotm 2020-05-13-20-30 uploaded (objtool warnings)

From: Christoph Hellwig
Date: Fri May 29 2020 - 09:57:56 EST

On Thu, May 28, 2020 at 07:20:05PM +0200, Peter Zijlstra wrote:
> > on x86_64:
> >
> > arch/x86/lib/csum-wrappers_64.o: warning: objtool: csum_and_copy_from_user()+0x2a4: call to memset() with UACCESS enabled
> > arch/x86/lib/csum-wrappers_64.o: warning: objtool: csum_and_copy_to_user()+0x243: return with UACCESS enabled
> Urgh, that's horrible code. That's got plain stac()/clac() calls on
> instead of the regular uaccess APIs.

Does it? If this is from the code in linux-next, then the code does a
user_access_begin/end in csum_and_copy_{from,to}_user, then uses
unsafe_{get,put}_user inside those function itself. But then they call
csum_partial_copy_generic with the __user casted away, but without any
comment on why this is safe.